Granular Cell Tumor of the Colon: A Rare Diagnosis in an Uncommon Location

Granular cell tumors (GCTs) are rare neoplasms of Schwann cell origin that typically exhibit benign behavior but can rarely undergo malignant transformation. Gastrointestinal involvement is uncommon, and colonic localization is particularly rare. We report the case of a 51-year-old African American woman referred for evaluation of iron-deficiency anemia. Colonoscopy revealed a 10-mm submucosal lesion at the hepatic flexure with a characteristic yellow-white appearance. Histopathologic examination showed polygonal cells with abundant granular eosinophilic cytoplasm and small, uniform nuclei. Immunohistochemical staining was strongly positive for S100, SOX10, and inhibin, confirming the diagnosis of a GCT. There was no evidence of necrosis or mitotic activity. Although the lesion lacked high-risk histologic features, given the tumor's submucosal origin and its uncertain malignant potential, future endoscopic resection will be pursued. This case demonstrates the importance of considering GCTs in the differential diagnosis of submucosal colonic lesions and highlights the diagnostic value of immunohistochemistry. It also emphasizes the need for surveillance in populations potentially at higher risk of malignancy, even in the absence of overt histologic features.